Printability Improving Agents And Papers Coated With Them

ABSTRACT

The present invention aims to provide printability improving agents and surface-treating agents capable of improving offset printability of papers, especially newsprint papers to be printed with offset inks as well as papers, especially newsprint papers that can be successfully printed with offset inks. According to a first aspect of the present invention, a printability improving agent comprising a cationic copolymer consisting of one or more hydrophobic monomer unit(s) selected from a specific group and a quaternary ammonium salt-containing monomer unit or a surface-treating agent comprising the printability improving agent and a water-soluble polymer material selected from a specific group is applied on the surface of a base paper, especially a newsprint base paper. According to a second aspect of the present invention, a hydrophobic monomer unit selected from a specific group and a quaternary ammonium salt-containing monomer unit is polymerized to give a cationic copolymer, which is then further polymerized with a hydrophobic monomer to give a copolymer. Alternatively, a hydrophobic monomer unit selected from a specific group and a quaternary ammonium salt-containing monomer unit is polymerized to give a cationic copolymer, which is further polymerized with a hydrophobic monomer in the presence of a surfactant to give a copolymer. A printability improving agent comprising the copolymer or a surface-treating agent comprising the printability improving agent and a water-soluble polymer material selected from a specific group is applied on the surface of a base paper, especially a newsprint base paper.

TECHNICAL FIELD

The present invention relates to printability improving agents, surface-treating agents, and papers, especially newsprint papers. More specifically, it relates to printability improving agents and surface-treating agents capable of improving offset printability of papers, especially newsprint papers to be printed with offset inks, as well as papers, especially newsprint papers, that can be successfully printed with offset inks.

BACKGROUND ART

Recent newsprint papers are required to have a lighter weight and a higher proportion of deinked pulp as well as to satisfy increasingly stricter requirements for printability in response to the accelerating trend toward offset printing, high-speed printing and color printing.

Conventional newsprint papers comprise newsprint base papers coated on their surfaces with solution-type surface sizing agents such as aqueous solutions of alkaline metal salts of styrene-maleic copolymers, aqueous solutions of alkaline metal salts of styrene-(meth)acrylic copolymers, and aqueous solutions of alkaline metal salts of α-olefin-maleic copolymers. Papers coated with these solution-type surface sizing agents show relatively good sizing performance, but insufficient printability with offset inks.

Thus, printability improving agents for offset inks comprising an emulsion obtained by polymerizing a hydrophobic monomer in the presence of a dispersant have been proposed (e.g., see patent document 1). These printability improving agents show printability improving effect better than that of the solution-type surface sizing agents but insufficient for papers having very low contents of internal sizing agents.

Patent document 1: JPA No. 2003-306887.

With the recent trend toward using a small amount of internal sizing agents, or none at all, in newsprint papers due to operational issues, there are demands for printability improving agents having high printability improving effect for such papers with low sizing degrees.

On the other hand, conventional printing inks based on petroleum solvents containing aromatic components have been rapidly replaced by ecological inks in recent years for environmental reasons, such as concern about influences of these components evaporating during their preparation or use on the environment or human bodies. However, newsprint papers coated with the solution-type surface sizing agents were not sufficient in printability when they were printed with ecological inks based on non-petroleum solvents such as vegetable oils or hydrogenated mineral oils.

Moreover, fountain solution wetting the coated surfaces of newsprint papers coated with the solution-type surface sizing agents during offset printing tend to invite redissolution of the surface sizing agents or dissolution of modified starches included therein, which may result in printing troubles such as fouling of blankets or plates.

Currently, dominant newsprint papers among offset printing papers are acidic, but will be neutral in future. However, the solution-type surface sizing agents do not have sufficient sizing effect on these neutral printing papers and must be increased to prevent out-of-register colors in multicolor printing, which may further deteriorate printability.

DISCLOSURE OF THE INVENTION

Problems to Be Solved By the Invention

The present invention aims to provide printability improving agents and surface-treating agents capable of improving offset printability of papers, especially newsprint papers to be printed with offset inks as well as papers, especially newsprint papers that can be successfully printed with offset inks.

Means to Solve the Problems

According to a first aspect of the invention, a printability improving agent comprising a cationic copolymer comprising one or more hydrophobic monomer unit(s) selected from the group consisting of:

(1) alkyl acrylates and/or alkyl methacrylates

(2) dialkyl diesters

(3) vinyl esters

(4) N-alkyl acrylamides and/or N-alkyl methacrylamides

(5) methyl vinyl ethers

and a quaternary ammonium salt-containing monomer unit or a surface-treating agent comprising the printability improving agent and a water-soluble polymer material selected from a specific group, is applied on the surface of a base paper, especially a newsprint base paper.

According to a second aspect of the present invention, a hydrophobic monomer unit selected from the group consisting of:

(1) styrenes

(2) alkyl acrylates and/or alkyl methacrylates

(3) dialkyl diesters

(4) vinyl esters

(5) N-alkyl acrylamides and/or N-alkyl methacrylamides

(6) methyl vinyl ethers

and a quaternary ammonium salt-containing monomer unit are polymerized to give a cationic copolymer [A-1], which is then further polymerized with a hydrophobic monomer [B] selected from the group shown above to give a copolymer. Alternatively, a hydrophobic monomer unit selected from the group shown above and a quaternary ammonium salt-containing monomer unit are polymerized to give a cationic copolymer, which is further polymerized with a hydrophobic monomer [B] selected from the group shown above to give a copolymer in the presence of a surfactant. A printability improving agent comprising the copolymer or a surface-treating agent comprising the printability improving agent and a water-soluble polymer material selected from a specific group is applied on the surface of a base paper, especially a newsprint base paper.

ADVANTAGES OF THE INVENTION

Papers having improved adhesion to offset inks, especially ecological inks and reduced starch dissolution, and consequently high printability and fewer printing troubles such as plate fouling can be provided by applying a printability improving agent of the present invention or a surface-treating agent containing the printability improving agent on the surface of a base paper.

THE MOST PREFERRED EMBODIMENTS OF THE INVENTION

First, the printability improving agent used in the first aspect of the present invention is explained. The printability improving agent comprises a cationic copolymer comprising at least a hydrophobic monomer unit and a quaternary ammonium salt-containing monomer unit as described below, wherein the “monomer unit” refers to a structural unit of a monomer when it is copolymerized. The hydrophobic monomer unit constituting this cationic copolymer is obtained by using a hydrophobic monomer during copolymerization. The quaternary ammonium salt-containing monomer unit is obtained by using a quaternary ammonium salt-containing monomer during copolymerization, or by copolymerizing an amino group-containing monomer and then converting thus obtained copolymer into a quaternary ammonium salt with a quaternizing agent. For example, a cationic copolymer can be obtained by copolymerizing a hydrophobic monomer and a tertiary amino group-containing monomer and then reacting thus obtained copolymer with a quaternizing agent. In addition to the hydrophobic monomer forming the hydrophobic monomer unit, the quaternary ammonium salt-containing monomer forming the quaternary ammonium-containing monomer unit and/or the amino group-containing monomer capable of being quaternized after copolymerization, the cationic copolymer can contain a nonionic monomer unit or an anionic monomer unit partially replacing the hydrophobic monomer unit, so long as the intended effect of the present invention is obtained.

Hydrophobic monomers used to form the hydrophobic monomer unit specifically include the following members, and these various hydrophobic monomers can be used alone or in combinations of two or more.

(1) alkyl(meth)acrylates: e.g., methyl(meth)acrylate, ethyl(meth)acrylate, normal butyl(meth)acrylate, isobutyl(meth)acrylate, tertiary butyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, lauryl(meth)acrylate, stearyl(meth)acrylate, cyclic alkyl(meth)acrylates, etc.;

(2) dialkyl diesters: e.g., dimethyl esters, diethyl esters and the like of maleic acid, fumaric acid, etc.;

(3) vinyl esters: e.g., vinyl esters of tertiary carboxylic acids containing 5-10 carbon atoms, vinyl propionate, etc.;

(4) N-alkyl(meth)acrylamides;

(5) methyl vinyl ethers.

Among them, alkyl(meth)acrylates are preferably used, in terms of printability.

Nonionic monomers that can be used to form the nonionic monomer unit capable of partially replacing the hydrophobic monomer unit include polymerizable monomers having neither cationic nor anionic group but having a hydrophilic group, e.g., (meth)acrylamides; acrylonitrile; hydroxyalkyl(meth)acrylates such as 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, 2,3-dihydroxypropyl(meth)acrylate, etc. These nonionic monomers can be used alone or in combinations of two or more.

Monomers used to form the quaternary ammonium salt-containing monomer unit include primary to tertiary amino group-containing monomers and quaternary ammonium salt-containing monomers, wherein the primary to tertiary amino group-containing monomers form quaternary ammonium salts with a quaternizing agent after copolymerization. Among them, preferred are quaternary ammonium salt-containing monomer units obtained by copolymerizing quaternary ammonium salt-containing monomers, and quaternary ammonium salt-containing monomer units obtained by copolymerizing tertiary amino group-containing monomers and then quaternizing the tertiary amino group.

Primary amino group-containing monomers include e.g., allylamine and methallylamine, and secondary amino group-containing monomers include e.g., diallylamine and dimethallylamine.

Tertiary amino group-containing monomers include tertiary amino group-containing vinyl compounds, specifically the following compounds, which can be used alone or in combinations of two or more.

(1) (dialkyl)aminoalkyl(meth)acrylates: e.g., dimethyl aminoethyl(meth)acrylate, diethyl aminoethyl(meth)acrylate, dimethyl aminopropyl(meth)acrylate, diethyl aminopropyl(meth)acrylate, etc.;

(2) (dialkyl)aminohydroxyalkyl(meth)acrylates: e.g., dimethyl aminohydroxyethyl(meth)acrylate, diethyl aminohydroxyethyl(meth)acrylate, dimethyl aminohydroxypropyl(meth)acrylate, diethyl aminohydroxypropyl(meth)acrylate, etc.;

(3) (dialkyl)aminoalkyl(meth)acrylamides: e.g., dimethyl aminopropyl(meth)acrylamide, diethyl aminopropyl(meth)acrylamide, etc.;

(4) vinyl pyridines;

(5) vinyl imidazoles.

Among them, (dialkyl)aminoalkyl(meth)acrylates and (dialkyl)aminoalkyl(meth)acrylamides are preferred, in terms of printability performance.

Quaternary ammonium salt-containing monomers include the tertiary amino group-containing monomers quaternized with a quaternizing agent. Quaternizing agents used to obtain the quaternary ammonium salt-containing monomers include epoxy compounds and organic halides such as methyl chloride, ethyl chloride, benzyl chloride, epichlorohydrin, alkylene oxides, styrene oxide, glycidyl trimethylammonium chloride, and 3-chloro-2-hydroxyammonium chloride; dimethyl sulfate, and diethyl sulfate. Among them, epichlorohydrin, alkylene oxides and styrene oxide are preferred, in terms of performance. These quaternizing agents can also be used after the tertiary amino group-containing monomers have been polymerized.

The weight ratio of the hydrophobic monomer unit and the quaternary ammonium salt-containing monomer unit forming the cationic copolymer in the printability improving agent according to the first aspect of the present invention is preferably 55-85:45-15, more preferably 60-80:40-20. If the cationic monomer unit is less than 15% or exceeds 45%, printability may be deteriorated.

The cationic copolymer used in the printability improving agent according to the first aspect of the present invention can be prepared by applying previously known polymerization methods, such as e.g., solution polymerization using an organic solvent, bulk polymerization using no solvent, emulsion polymerization in an aqueous system using an oligomer or polymer emulsifier, etc.

The cationic copolymer can be obtained by e.g., polymerizing a mixture of the hydrophobic monomer and the tertiary amino group-containing monomer, or a mixture of the hydrophobic monomer and the quaternary ammonium salt-containing monomer or a mixture of such a mixture and one of other copolymerizable vinyl monomers in a lower alcohol organic solvent such as methyl alcohol, ethyl alcohol or isopropyl alcohol, or in an organic oily solvents such as benzene, toluene or xylene, or in a mixed solution of such a lower alcohol organic solvent and water, or in water, or in a solvent-free system at 60-130° C. for 1-10 hours using a free-radical polymerization catalyst, and after completion of the polymerization, distilling the organic solvent off if needed and quaternizing the tertiary amino group by a known and common method.

Free-radical polymerization catalysts include, but are not limited to, e.g., oil-soluble azo catalysts such as 2,2′-azobisisobutyronitrile, dimethyl 2,2′-azobis(2-methyl propionate); oil-soluble organic peroxides such as benzyl peroxide, tertiary butyl peroxybenzoate, tertiary butyl peroxy-2-ethyl hexanoate; persulfates such as ammonium persulfate, potassium persulfate, sodium persulfate; water-soluble peroxides such as hydrogen peroxide; redox polymerization catalysts formed by combination of these persulfates and peroxides with reducing agents; water-soluble azo catalysts such as 2,2′-azobis(2-amidinopropane)dihydrochloride; water-soluble organic peroxides such as tertiary butyl hydroperoxide.

If desired, known chain transfer agents such as alkyl mercaptans may also be used. It should be noted that the monomer used to synthesize the cationic copolymer in the printability improving agent according to the first aspect of the present invention is substantially completely reacted to form a monomer unit in the cationic copolymer.

Alkaline materials preferably used for coating with the printability improving agent according to the first aspect of the present invention include e.g., ammonia; alkyl amines; aminoalcohols such as monoethanolamine, diethanolamine, triethanolamine; inorganic alkalis such as sodium hydroxide, potassium hydroxide; sulfites; carbonates; organic acid salts, etc.

Next, the printability improving agent used in the second aspect of the present invention is explained. The printability improving agent comprises at least a copolymer obtained by polymerizing a specific hydrophobic monomer unit and a quaternary ammonium salt-containing monomer unit to give a cationic copolymer [A-1], which is then further polymerized with a specific hydrophobic monomer [B], or a copolymer obtained by polymerizing the cationic copolymer [A-1] with a specific hydrophobic monomer [B] in the presence of a surfactant [A-2]. Preferably, it comprises a copolymer obtained by polymerizing the cationic copolymer [A-1] with a specific hydrophobic monomer [B] in the presence of a surfactant [A-2].

1. Cationic Copolymer [A-1]

The “monomer unit” refers to a structural unit of a monomer when it is copolymerized. The hydrophobic monomer unit forming the cationic copolymer [A-1] is obtained by using a hydrophobic monomer during copolymerization. The quaternary ammonium salt-containing monomer unit is obtained by using a quaternary ammonium salt-containing monomer during copolymerization, or by copolymerizing an amino group-containing monomer and then converting thus obtained copolymer into a quaternary ammonium salt with a quaternizing agent. For example, a cationic copolymer can be obtained by copolymerizing a hydrophobic monomer and a tertiary amino group-containing monomer and then reacting thus obtained copolymer with a quaternizing agent. In addition to the hydrophobic monomer forming the hydrophobic monomer unit, the quaternary ammonium salt-containing monomer forming the quaternary ammonium-containing monomer unit and/or the amino group-containing monomer capable of being quaternized after copolymerization, the cationic copolymer can contain a nonionic monomer unit or an anionic monomer unit partially replacing the hydrophobic monomer unit, so long as the intended effect of the present invention is obtained.

Hydrophobic monomers used to form the hydrophobic monomer unit of the cationic copolymer [A-1] specifically include the following members, and these various hydrophobic monomers can be used alone or in combinations of two or more.

(1) styrenes: e.g., styrene, α-methyl styrene, vinyl toluene, divinyl benzene, etc.;

(2) alkyl(meth)acrylates: e.g., methyl(meth)acrylate, ethyl(meth)acrylate, normal butyl(meth)acrylate, isobutyl(meth)acrylate, tertiary butyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, lauryl(meth)acrylate, stearyl(meth)acrylate, cyclic alkyl(meth)acrylates, etc.;

(3) dialkyl diesters: e.g., dimethyl esters, diethyl esters and the like of maleic acid, fumaric acid, etc.;

(4) vinyl esters: e.g., vinyl esters of tertiary carboxylic acids containing 5-10 carbon atoms, vinyl propionate, etc.;

(5) N-alkyl(meth)acrylamides;

(6) methyl vinyl ethers.

Among them, the styrenes and alkyl(meth)acrylates are preferably used alone or in combination, especially alkyl(meth)acrylates alone in terms of stability of the printability improving agent and printability.

Nonionic monomers that can be used to form the nonionic monomer unit capable of partially replacing the hydrophobic monomer unit include polymerizable monomers having neither cationic nor anionic group but having a hydrophilic group, e.g., (meth)acrylamides; acrylonitrile; hydroxyalkyl(meth)acrylates such as 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, 2,3-dihydroxypropyl(meth)acrylate, etc. These nonionic monomers can be used alone or in combinations of two or more.

Monomers used to form the quaternary ammonium salt-containing monomer unit that can be used for the preparation of the cationic copolymer [A-1] include primary to tertiary amino group-containing monomers and quaternary ammonium salt-containing monomers, wherein the primary to tertiary amino group-containing monomers form quaternary ammonium salts with a quaternizing agent after copolymerization. Among them, preferred are quaternary ammonium salt-containing monomer units obtained by copolymerizing quaternary ammonium salt-containing monomers and quaternary ammonium salt-containing monomer units obtained by copolymerizing tertiary amino group-containing monomers and then quaternizing the tertiary amino group.

Primary amino group-containing monomers include e.g., allylamine and methallylamine, and secondary amino group-containing monomers include e.g., diallylamine and dimethallylamine.

Tertiary amino group-containing monomers include tertiary amino group-containing vinyl compounds, specifically the following compounds, which can be used alone or in combinations of two or more.

(1) (dialkyl)aminoalkyl(meth)acrylates: e.g., dimethyl aminoethyl(meth)acrylate, diethyl aminoethyl(meth)acrylate, dimethyl aminopropyl(meth)acrylate, diethyl aminopropyl(meth)acrylate, etc.;

(2) (dialkyl)aminohydroxyalkyl(meth)acrylates: e.g., dimethyl aminohydroxyethyl(meth)acrylate, diethyl aminohydroxyethyl(meth)acrylate, dimethyl aminohydroxypropyl(meth)acrylate, diethyl aminohydroxypropyl(meth)acrylate, etc.;

(3) (dialkyl)aminoalkyl(meth)acrylamides: e.g., dimethyl aminopropyl(meth)acrylamide, diethyl aminopropyl(meth)acrylamide, etc.;

(4) vinyl pyridines;

(5) vinyl imidazoles.

Among them, (dialkyl)aminoalkyl(meth)acrylates and (dialkyl)aminoalkyl(meth)acrylamides are preferred in terms of printability performance.

Quaternary ammonium salt-containing monomers include the tertiary amino group-containing monomers quaternized with a quaternizing agent. Quaternizing agents used to obtain the quaternary ammonium salt-containing monomers include epoxy compounds and organic halides such as methyl chloride, ethyl chloride, benzyl chloride, epichlorohydrin, alkylene oxides, styrene oxide, glycidyl trimethylammonium chloride, and 3-chloro-2-hydroxyammonium chloride; dimethyl sulfate, and diethyl sulfate. Among them, epichlorohydrin, alkylene oxides and styrene oxide are preferred in terms of performance. These quaternizing agents can also be used after the tertiary amino group-containing monomers have been polymerized.

Quaternizing agents used to quaternize the tertiary amino group-containing monomer after copolymerization include organic halides such as methyl chloride, ethyl chloride, benzyl chloride, epichlorohydrin, glycidyl trimethyl ammonium chloride, and 3-chloro-2-hydroxyammonium chloride; dimethyl sulfate and diethyl sulfate.

The cationic copolymer [A-1] can be obtained by e.g., polymerizing (1) a mixture of the hydrophobic monomer and the tertiary amino group-containing monomer, or (2) a mixture of the hydrophobic monomer and the quaternary ammonium salt-containing monomer in a lower alcohol organic solvent such as methyl alcohol, ethyl alcohol or isopropyl alcohol, or in an organic oily solvent such as benzene, toluene or xylene, or in a mixed solution of such a lower alcohol organic solvent and water, or in water at 60-130° C. for 1-10 hours using a free-radical polymerization catalyst, and after completion of the polymerization, distilling the organic solvent off if needed and quaternizing the tertiary amino group by a known and common method.

Free-radical polymerization catalysts include, but are not limited to, e.g., oil-soluble azo catalysts such as 2,2′-azobisisobutyronitrile, dimethyl 2,2′-azobis(2-methyl propionate); oil-soluble organic peroxides such as benzyl peroxide, tertiary butyl peroxybenzoate, tertiary butyl peroxy-2-ethyl hexanoate; persulfates such as ammonium persulfate, potassium persulfate, sodium persulfate; water-soluble peroxides such as hydrogen peroxide; redox polymerization catalysts formed by combination of these persulfates and peroxides with reducing agents; water-soluble azo catalysts such as 2,2′-azobis(2-amidinopropane)dihydrochloride; water-soluble organic peroxides such as tertiary butyl hydroperoxide.

If desired, known chain transfer agents such as alkyl mercaptans may also be used. It should be noted that the monomer used to synthesize the cationic copolymer [A-1] in the printability improving agent according to the second aspect of the present invention is substantially completely reacted to form a monomer unit in the cationic copolymer [A-1].

The weight ratio of the hydrophobic monomer unit and the quaternary ammonium salt-containing monomer unit in the cationic copolymer [A-1] is preferably 40-85:60-15, more preferably 50-85:50-15. If the cationic monomer unit is less than 15% or exceeds 60%, printability may be deteriorated.

2. Surfactant [A-2]

The surfactant [A-2] optionally used in the printability improving agent according to the second aspect of the present invention can be a known emulsifier or dispersant that can be normally applied for emulsion polymerization, such as e.g., cationic, nonionic, ampholytic and anionic surfactants, and free-radically polymerizable surfactants, and at least one member selected from these groups can be used.

Cationic surfactants that can be used include acetate salts and epichlorohydrin-modified products of primary and secondary amines, etc. Primary and secondary amines are represented by general formulae R₁NH₂ and R₂R₃NH, wherein R₁, R₂ and R₃ each represent the same or different linear or cyclic hydrocarbon group containing 1-30 carbon atoms. R₁, R₂ and R₃ include e.g., substituents such as methyl, ethyl, propyl, isopropyl, allyl, butyl, isobutyl, S-butyl, t-butyl, hexyl, cyclohexyl, octyl, 2-ethylhexyl, nonyl, decyl, lauryl, myristyl, palmityl, stearyl, oleyl, phenyl, naphthyl, dehydroabietyl, etc.

Other cationic surfactants include tetraalkylammonium chlorides, trialkylbenzylammonium chlorides, acetate salts and epichlorohydrin-modified products of rosin amines, monooxyethylene alkylamines and polyoxyethylene alkylamines. These cationic oligomer surfactants can be used alone or in combinations of two or more.

Nonionic surfactants include e.g., polyoxyalkylene alkyl phenyl ethers, polyoxyalkylene alkyl ethers, polyoxyalkylene fatty acid esters, polyoxypropylene polyoxyethylene glycol glycerin fatty acid esters, sorbitan fatty acid esters, polyethylene glycol fatty acid esters, polyoxyethylene sorbitan fatty acid esters, sucrose fatty acid esters, pentaerythritol fatty acid esters, propylene glycol fatty acid esters, fatty acid diethanolamides, and polyoxypropylene polyoxyethylene glycol. These nonionic surfactants can be used alone or in combinations of two or more.

Anionic surfactants include e.g., phosphate ester salts, sulfonate salts, succinate ester salts and sulfosuccinate ester salts of polyoxyalkylene alkyl phenyl ethers, polyoxyalkylene monostyryl phenyl ethers, polyoxyalkylene distyryl phenyl ethers, polyoxyalkylene alkyl ethers and polyoxyalkylene fatty acid esters, etc.; and alkylbenzene sulfonate, alkaline salts of naphthalene sulfonate-formalin condensation products, alkenyl succinate salts, alkaline metal salts of rosin and alkaline metal salts of fortified rosin. These anionic surfactants can be used alone or in combinations of two or more.

The free-radically polymerizable surfactants are generally called reactive emulsifiers, which are compounds having a hydrophobic group, a hydrophilic group and a carbon-carbon double bond. The compounds having a carbon-carbon double bond include e.g., compounds having a functional group such as (meth)allyl, 1-propenyl, 2-methyl-1-propenyl, isopropenyl, vinyl, and (meth)acryloyl groups.

These free-radically polymerizable surfactants that can be used are those normally applicable for emulsion polymerization, and include, but are not limited to, e.g., polyoxyalkylene alkyl ethers, polyoxyalkylene aralkyl ethers, polyoxyalkylene phenyl ethers, polyoxyalkylene monostyryl phenyl ethers and polyoxyalkylene distyryl phenyl ethers having one or more of the functional groups in the molecule, and sulfonate salts, sulfate ester salts, phosphate ester salts and sulfosuccinate ester salts thereof; fatty acid carboxylate salts and aromatic carboxylate salts of polyoxyalkylene alkyl ethers or polyoxyalkylene phenyl ethers having one or more of the functional groups in the molecule; acidic(meth)acrylate ester compounds; rosin-glycidyl(meth)acrylate compounds; alkyl diphenyl ether disulfonate compounds, e.g., hexyl diphenyl ether disulfonate, decyl diphenyl ether disulfonate, dodecyl diphenyl ether disulfonate, hexadecyl diphenyl ether disulfonate and alkaline metal salts such as sodium salts, potassium salts or ammonium salts thereof. These surfactants having polymerizable groups can be used alone or in combinations of two or more.

In the printability improving agent according to the second aspect of the present invention, at least one member selected from the group consisting of the cationic surfactants, nonionic surfactants and free-radically polymerizable nonionic surfactants is preferably used in view of printability, stability during emulsion polymerization and compatibility with other concomitant chemicals.

The cationic surfactants, nonionic surfactants and free-radically polymerizable nonionic surfactants preferably contain a long-chain alkyl group and a polyalkylene oxide group in terms of stability during preparation, more preferably an alkyl group containing 6-22 carbon atoms and a polyethylene oxide group having 5-40 EO moles in terms of the stability of the printability improving agent, printability and compatibility with other concomitant chemicals.

3. Hydrophobic Monomer [B]

The printability improving agent according to the second aspect of the present invention can be obtained by emulsion polymerizing a hydrophobic monomer [B] in the presence of the cationic copolymer [A-1] consisting of at least a hydrophobic monomer unit and a quaternary ammonium salt-containing monomer unit or the cationic copolymer [A-1] and the surfactant [A-2]. Suitable hydrophobic monomers [B] are similar to those listed for the cationic copolymer [A-1].

Specifically, examples include styrenes such as styrene, α-methyl styrene, vinyl toluene, divinyl benzene; alkyl(meth)acrylates having an alkyl group containing 1-18 carbon atoms such as methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, butyl(meth)acrylate, octyl(meth)acrylate, 2-ethylhexyl(meth)acrylate; cyclic alkyl(meth)acrylates such as cyclohexyl(meth)acrylates, benzyl(meth)acrylate; dialkyl diesters of maleic acid and fumaric acid; vinyl esters such as vinyl acetate and vinyl propionate; N-alkyl(meth)acrylamides; and methyl vinyl ethers; and one or more of them can be used.

Among the hydrophobic monomers [B], styrenes and alkyl(meth)acrylates are preferred in terms of printability and stability of the printability improving agent.

In addition to the hydrophobic monomers mentioned above, other copolymerizable monomers such as nonionic monomers can be used in a range of 20 mol % or less. Nonionic monomers include polymerizable monomer having neither cationic nor anionic group and having a hydrophilic group, e.g., (meth)acrylamides, acrylonitrile, and hydroxyalkyl(meth)acrylates, e.g., 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, and 2,3-dihydroxypropyl(meth)acrylate. These nonionic monomers can be used alone or in combinations of two or more.

When the hydrophobic monomer [B] is polymerized in the presence of the cationic copolymer [A-1] consisting of at least a hydrophobic monomer unit and a quaternary ammonium salt-containing monomer unit or the cationic copolymer [A-1] and the surfactant [A-2], the weight ratio of the cationic copolymer [A-1] or the cationic copolymer [A-1] plus surfactant [A-2] and the hydrophobic monomer [B] is preferably chosen in such a manner that 30-100 parts by weight of the cationic copolymer [A-1] is contained per 100 parts by weight of the hydrophobic monomer [B] in terms of the stability of the resulting emulsion. Especially, 40-100 parts by weight of the cationic copolymer [A-1] component is preferably contained in terms of sizing performance.

The weight ratio of the hydrophobic monomer [B] and the surfactant [A-2] is chosen in such a manner that normally 0-10 parts by weight, especially 1-5 parts by weight of the surfactant [A-2] is contained per 100 parts by weight of the hydrophobic monomer [B]. If more than 10 parts by weight of the surfactant [A-2] is contained per 100 parts by weight of the hydrophobic monomer [B], printability may not be sufficiently improved.

The hydrophobic monomer [B] component can be polymerized by previously known emulsion polymerization methods, e.g., by emulsion polymerizing the hydrophobic monomer [B] component in water in the presence of a mixture of the cationic copolymer [A-1] and the surfactant [A-2] using a free-radical polymerization catalyst. It should be noted that the hydrophobic monomer [B] component is substantially completely polymerized to form a copolymer.

Polymerization catalysts used for the polymerization reaction include e.g., persulfates such as ammonium persulfate, potassium persulfate, sodium persulfate; redox polymerization catalysts formed by combination of these persulfates with reducing agents; water-soluble azo catalysts such as 2,2′-azobis(2-amidinopropane)dihydrochloride; or organic peroxides such as tertiary butyl hydroperoxide. In addition, oil-soluble azo catalysts such as 2,2′-azobisisobutyronitrile, dimethyl 2,2′-azobis(2-methyl propionate); or oil-soluble organic peroxides such as benzyl peroxide, tertiary butyl peroxybenzoate, tertiary butyl peroxy-2-ethyl hexanoate can be used in combination with the water-soluble free radical initiators mentioned above. If desired, known chain transfer agents such as alkyl mercaptans may also be used without inconvenience.

During the emulsion polymerization of the hydrophobic monomer [B] component, known oligomer surfactants and polymer dispersants can also be used without inconvenience, so long as the performance of the printability improving agent according to the second aspect of the present invention is not impaired.

Alkaline materials preferably used for coating with the printability improving agent according to the second aspect of the present invention include e.g., ammonia; alkyl amines; aminoalcohols such as monoethanolamine, diethanolamine, triethanolamine; inorganic alkalis such as sodium hydroxide, potassium hydroxide; sulfites; carbonates; organic acid salts, etc.

The ecological inks described below refer to printing inks using only solvents having little environmental impact containing 1% or less of aromatic components such as aromatic hydrocarbons, and include e.g., inks using animal or vegetable solvents such as soybean oil inks, aromatic-free inks using aromatic-free solvents, etc. Methods for printing newsprint papers with such ecological inks include offset printing, etc.

The printability improving agent according to the first or second aspect of the present invention is applied on various base papers directly or after it has been mixed with a binder consisting of a water-soluble polymer material to form a surface-treating agent in the same manner as in normal paper-making processes. The surface-treating agent refers to a mixed coating solution containing the printability improving agent, water-soluble polymer material, and other chemicals.

Water-soluble polymer materials include e.g., various modified starches such as enzyme-modified starches, thermochemically modified starches, oxidized starches, esterified starches, etherified starches (e.g., hydroxyethylated starches, etc.), cationized starches; polyvinyl alcohols such as polyvinyl alcohols, completely saponified polyvinyl alcohols, partially saponified polyvinyl alcohols, carboxyl-modified polyvinyl alcohols, silanol-modified polyvinyl alcohols, cationically modified polyvinyl alcohols, terminally alkylated polyvinyl alcohols; and cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose. These are used alone or in combinations of two or more.

The printability improving agent according to the first or second aspect of the present invention may contain additives such as anti-tack agents, preservatives, antifoaming agents, lubricants, anti-slip agents, anti-rust agents, UV protective agents, anti-fading agents, fluorescent whitening agents, viscosity stabilizers, alkaline materials, etc. or other surface sizing agents, so long as the effect of the printability improving agent is not impaired. Among them, alkaline materials are preferably used because printability with offset inks is improved.

Papers coated with the printability improving agent according to the first or second aspect of the present invention or a surface-treating agent containing the printability improving agent, are explained. The printability improving agent or a surface-treating agent containing the printability improving agent is applied on the surface of a base paper prepared by an acidic or neutral papermaking process. Various types of base papers can be used, such as coated base paper, PPC paper, inkjet paper, business form, woodfree paper, wood containing paper, coated board, liner board, heat-sensitive transfer paper, etc.

The pulp material for the base paper is not specifically limited. Bleached or unbleached mechanical pulps such as groundwood pulp (GP), mechanical pulp (MP), thermomechanical pulp (TMP); bleached or unbleached chemical pulps such as kraft pulp (KP), sulfite pulp; or recycled pulps such as deinked pulp (DIP) can be blended in appropriate proportions and used depending on the type of the base paper to be prepared.

If desired, fillers may be added during the preparation of the base paper depending on the properties required for the paper including optical properties such as opacity, printing opacity and brightness or paper quality such as smoothness. Fillers that can be optionally used are those commonly used in acidic or neutral papermaking processes and are not specifically limited. In neutral papermaking processes, for example, inorganic fillers such as clay, calcined kaolin, delaminated kaolin, ground calcium carbonate, precipitated calcium carbonate, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, and zinc hydroxide; or organic fillers such as urea-formalin resins, polystyrene resins, phenol resins and hollow microparticles can be used alone or as appropriate combinations of two or more of them. In acidic papermaking processes, the fillers listed above for use in neutral papermaking processes except for acid-soluble ones can be used alone or in appropriate combinations of two or more.

Internal sizing agents or internal paper additives may also be contained, and such internal paper additives include aluminum sulfate, aluminum chloride, sodium aluminate; basic aluminum compounds such as basic aluminum chloride and basic aluminum polyhydroxide; water-soluble aluminum compounds such as colloidal alumina readily soluble in water; polyvalent metal compounds such as ferrous sulfate and ferric sulfate; colloidal silica, etc.

Other paper additives that can be used include various compounds, such as various starches, polyacrylamides, urea resins, melamine resins, epoxy resins, polyamide resins, polyamides, polyamine resins, polyamines, polyethyleneimine, vegetable gums, polyvinyl alcohols, latexes, polyethylene oxide, hydrophilic crosslinked polymer particle dispersions and derivatives or modified products thereof.

In addition, internal paper additives such as dyes, fluorescent whitening agents, pH adjusting materials, antifoaming agents, pitch control agents, slime control agents or the like can also be contained as appropriate depending on the purpose.

Base papers prepared by neutral papermaking processes are more preferable than base papers prepared by acidic papermaking processes because the effect of the printability improving agent of the present invention becomes more visible.

The solids concentration of the printability improving agent according to the first or second aspect in the surface-treating agent (coating solution) is normally 0.05-2% by weight, preferably 0.1-1% by weight. If it is less than 0.05% by weight, the printability improving effect may be insufficient, while concentrations exceeding 2% by weight are economically disadvantageous because the printability improving effect reaches its peak around 2% by weight.

The coating amount of the printability improving agent on the base paper is normally 0.005-0.3 g/m², preferably 0.01-0.2 g/m² on a solids basis. The printability is especially improved within this range.

When a surface-treating agent comprising a mixture of the printability improving agent and a water-soluble polymer material is to be applied, the solids concentration of the printability improving agent in the surface-treating agent and the coating amount are as described above, while the solids concentration of the water-soluble polymer material in the surface-treating agent and the coating amount of the water-soluble polymer material on the base paper are determined according to the target surface strength of the paper, which depends on the type of the paper. Thus, the ratio of the water-soluble polymer material and the surface coating sizing agent is not specifically defined.

The apparatus for applying the printability improving agent according to the first or second aspect of the present invention or a surface-treating agent containing the printability improving agent on the base paper is not specifically limited, and known apparatus such as size presses, gate roll coaters, Sym-Sizer size presses, blade coaters, bar coaters, air knife coaters, and knife coaters can be chosen and used as appropriate.

Newsprint papers coated with the printability improving agent according to the first or second aspect of the present invention or a surface-treating agent containing the printability improving agent are explained. Pulp materials may be those conventionally used for newsprint papers, including mechanical pulps (MP) such as groundwood pulp (GP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP) and semichemical pulp (SCP); chemical pulps (CP) such as kraft pulp (KP) and sulfite pulp (SP); deinked pulps (DIP) obtained by deinking waste paper containing these pulps; and recycled pulps obtained by disintegrating mill broke; and they are used alone or in admixture at given proportions and converted into paper by known and common machines. In view of demands for increasing the proportion of DIP consistent with the recent growing interest in environmental protection, the proportion of DIP is preferably in the range of 50-100% by weight.

Newsprint base papers can contain fillers such as white carbon, clay, silica, talc, titanium oxide, calcium carbonate and synthetic resin fillers (such as vinyl chloride resins, polystyrene resins, urea-formalin resins, melamine resins, styrene-butadiene copolymer resins, etc.), if desired. They may also contain internal paper strength enhancers such as polyacrylamide polymers, polyvinyl alcohol polymers, cationic starches, urea-formalin resins and melamine-formalin resins; drainage and/or retention aids such as salts of acrylamide-aminomethyl acrylamide copolymers, cationic starches, polyethyleneimine, polyethylene oxide and acrylamide-sodium acrylate copolymers; internal sizing agents such as rosin sizing agents, AKD, ASA, petroleum sizing agents, and neutral rosin sizing agents; and other additives such as UV protective agents, anti-fading agents, etc.

The printability improving agent of the present invention is applied on a newsprint base paper directly or after it has been mixed with a binder consisting of a water-soluble polymer material to form a surface-treating agent. Water-soluble polymer materials include e.g., various modified starches such as enzyme-modified starches, thermochemically modified starches, oxidized starches, esterified starches, etherified starches (e.g., hydroxyethylated starches, etc.), cationized starches; polyvinyl alcohols such as polyvinyl alcohols, completely saponified polyvinyl alcohols, partially saponified polyvinyl alcohols, carboxyl-modified polyvinyl alcohols, silanol-modified polyvinyl alcohols, cationically modified polyvinyl alcohols, terminally alkylated polyvinyl alcohols; and cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose. These are used alone or in combinations of two or more.

The printability improving agent or a surface-treating agent containing the printability improving agent can be applied on a newsprint base paper using a normal coater for papermaking. For example, suitable coaters include two-roll size presses, blade metering size presses, rod metering size presses, gate roll coaters, bar coaters, air-knife coaters, spray coaters, etc. Among them, film transfer coaters such as gate roll coaters are desirable and gate roll coaters (GRC) are most preferably used for newsprint papers.

The coating speed at which the printability improving agent or a surface-treating agent containing the printability improving agent is applied is not specifically limited, so long as it is within the range of the machine speed at which normal newspapers can be prepared, but normally 800-2500 m/min. By adopting a high coating speed of 800 m/min or more, much of the surface-treating agent remains near the surface to increase printability improving effect because the surface-treating agent is dried before it sufficiently penetrates paper layers.

The effect of the present invention is more remarkable when the printability improving agent or a surface-treating agent containing the printability improving agent is applied on newsprint base papers prepared by neutral papermaking processes, than on newsprint base papers prepared by acidic papermaking processes.

The solids concentration of the printability improving agent in the surface-treating agent (coating solution) is normally 0.05-2% by weight, preferably 0.1-1% by weight. If it is less than 0.05% by weight, the printability improving effect may be insufficient, while concentrations exceeding 2% by weight are economically disadvantageous because the printability improving effect reaches its peak around 2% by weight. The coating amount of the printability improving agent on the base paper is normally 0.005-0.3 g/m², preferably 0.01-0.2 g/m² on a solids basis. The printability is especially improved within this range.

When a surface-treating agent comprising a mixture of the printability improving agent and a water-soluble polymer material is to be applied, the solids concentration of the printability improving agent in the surface-treating agent and the coating amount are as described above, while the coating amount (per both sides) of the water-soluble polymer material is suitably in the range of 0.05-2.0 g/m². If the coating amount is less than 0.05 g/m², the surface strength of the newsprint paper may be insufficient. If the coating amount exceeds 2.0 g/m², however, there is a higher possibility of causing tack (i.e. so-called “neppari”), a typical issue of newsprint papers for offset printing (a trouble of stickiness caused by transfer and accumulation of a coating material on a blanket during mass printing of newspapers).

Newsprint papers of the present invention are preferably calendered to ensure paper thickness and smoothness suitable for offset printing after they have been coated with the printability improving agent according to the first or second aspect or a surface-treating agent containing the printability improving agent and dried. Suitable calenders include normal hard nip calenders or hot soft nip calenders (e.g., see “Paper and Pulp Technology Times”, Vol. 43, No. 1 (2000) p 23, etc.). Considering future weight reduction of newsprint papers, soft nip calenders are more preferably used for newsprint papers of the present invention. In terms of color printability, the printability improving agent of the present invention or a surface-treating agent containing the printability improving agent should be combined with soft nip calendering.

EXAMPLES

The following examples and comparative examples further illustrate the present invention without, however, limiting the invention thereto. Unless otherwise specified, “parts” and “%” used herein mean parts by weight and % by weight, respectively. Examples 1-29 and Comparative examples 1-6 relate to printability improving agents according to the first aspect of the present invention, while Examples 30-67 and Comparative examples 7-12 relate to printability improving agents according to the second aspect of the present invention.

Example 1

A 1-liter four-neck flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet tube was charged with 70 parts of 2-ethylhexyl methacrylate, 30 parts of dimethyl aminoethyl methacrylate, 2.5 parts of 2,2′-azobisisobutyronitrile and 44 parts of isopropyl alcohol, and maintained at 80° C. for 3 hours, and then 0.4 parts of 2,2′-azobisisobutyronitrile was added and the mixture was maintained at the same temperature for further 2 hours. Then, 12.7 parts of acetic acid (100 mol % relative to dimethyl aminoethyl methacrylate) and 251 parts of water were added, and isopropyl alcohol was distilled off. Then, 34 parts of water, and 17.7 parts of a quaternizing agent consisting of epichlorohydrin (100 mol % relative to dimethyl aminoethyl methacrylate) were added, and the mixture was maintained at 80° C. for 2 hours. Then, the mixture was diluted with water to give printability improving agent 1 having a solids content of 20.3%. It should be noted that substantially no uncopolymerized monomer remained, and that little unreacted epichlorohydrin used as a quaternizing agent remained.

Example 2

Printability improving agent 2 having a solids content of 20.5% was obtained by the same procedure as in Example 1 except that the monomer composition was as shown in Table 1 for Example 2 without using a quaternizing agent and that no quaternization reaction was performed.

Examples 3-9

Printability improving agents were obtained in the same manner as printability improving agent 1 except that the type and amount of the hydrophobic monomer, the type and amount of the tertiary amino group-containing monomer, and the type and amount of the quaternizing agent were varied as shown in Table 1. The solids contents of the resulting printability improving agents 3-9 are shown in Table 1.

[Table 1] TABLE 1 Quaternary ammonium salt-containing Solids Hydrophobic monomer unit monomer unit content Type Parts Type Parts Type Parts Type Parts % by weight % Example 1 EHMA 70.0 — — DM 30.0 ECH 17.7 40.5 20.3 Example 2 EHMA 67.5 MMA 10.0 DMC 22.5 — — 22.5 20.5 Example 3 EHMA 85.0 — — DM 15.0 ECH 8.8 21.9 20.3 Example 4 EHMA 40.0 BA 40.0 DPA 20.0 ECH 11.8 28.5 20.0 Example 5 EHMA 40.0 EHA 40.0 DPA 20.0 ECH 11.8 28.5 20.5 Example 6 EHMA 40.0 IBMA 40.0 DPA 20.0 BTO 9.2 26.8 20.2 Example 7 EHMA 40.0 BA 40.0 DM 20.0 STO 15.3 30.8 20.3 Example 8 EHMA 60.0 — — DM 40.0 ECH 23.5 51.4 20.3 Example 9 EHMA 90.0 — — DM 10.0 ECH 5.9 15.0 20.0

In Table 1, abbreviations have the meanings below:

EHMA: 2-ethylhexyl methacrylate, MMA: methyl methacrylate, BA: normal butyl acrylate, EHA: 2-ethylhexyl acrylate, IBMA: isobutyl methacrylate, DM: dimethyl aminoethyl methacrylate, DMC: dimethyl aminoethyl methacrylate quaternized with methyl chloride, DPA: dimethyl aminopropyl acrylamide, ECH: epichlorohydrin, BTO: butylene oxide, STO: styrene oxide.

Synthesis Example 1 for Comparative Examples

A 1-liter four-neck flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet tube was charged with 44 parts of toluene, 50 parts of diisobutylene, 50 parts of maleic anhydride and 3.3 parts of 2,2′-azobisisobutyronitrile, and the mixture was heated with stirring to a temperature of 80° C. Then, the mixture was aged for 3 hours to complete the reaction. Then, 82 parts of a 48% aqueous potassium hydroxide solution (50 mol % relative to maleic anhydride), and 251 parts of water were added, and toluene was distilled off. Then, a 48% aqueous potassium hydroxide solution was added to a total of 100 mol % relative to maleic anhydride, and the solution was diluted with water to a copolymer concentration of 20% to give an aqueous potassium hydroxide solution of a water-soluble diisobutylene-maleic anhydride copolymer (printability improving agent 10 (for comparative examples)). The monomer composition ratio in the polymer was diisobutylene:maleic anhydride=50:50 by weight.

Synthesis Example 2 for Comparative Examples

A 1-liter four-neck flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet tube was charged with 35 parts of water, 65 parts of 95% isopropyl alcohol, a mixed monomer solution of 60 parts of styrene and 40 parts of maleic anhydride, and 3 parts of 2,2′-azobisisobutyronitrile, and the contents of the flask were heated with stirring to a temperature of 80° C. Then, the mixture was aged for 4 hours to complete the reaction. Then, isopropyl alcohol was distilled off, and after cooling, 50 parts of a 28% aqueous ammonia solution (100 mol % relative to maleic anhydride) was added, and the solution was diluted with water to a copolymer concentration of 20% to give an aqueous ammonia solution of a water-soluble styrene-maleic copolymer (printability improving agent 11 (for comparative examples)). The monomer composition ratio in the polymer was styrene:maleic anhydride=60:40 by weight.

Synthesis Example 3 for Comparative Examples

A 1-liter four-neck flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet tube was charged with 35 parts of water, 65 parts of 95% isopropyl alcohol, a mixed monomer solution of 70 parts of styrene and 30 parts of acrylic acid, and 3 parts of 2,2′-azobisisobutyronitrile, and the contents of the flask were heated with stirring to a temperature of 80° C. Then, the mixture was aged for 4 hours to complete the reaction. Then, isopropyl alcohol was distilled off, and after cooling, 25.3 parts of a 28% aqueous ammonia solution (100 mol % relative to maleic anhydride) was added, and the solution was diluted with water to a copolymer concentration of 20% to give an aqueous ammonia solution of a water-soluble styrene-acrylic copolymer (printability improving agent 12 (for comparative example)). The monomer composition ratio in the polymer was styrene:acrylic acid=70:30 by weight.

Preparation of Newsprint Base Papers

(1) Preparation of an Acidic Newsprint Base Paper

To a deinked pulp slurry having a Canadian Standard Freeness (CSF) of 160 and a concentration of 2.5% were successively added 15% (bone dry weight basis) relative to pulp of talc (ND talc available from FUJI TALC INDUSTRIAL CO., LTD.), 1.5% (bone dry weight basis) relative to pulp of aluminum sulfate, and 0.05% (bone dry weight basis) relative to pulp of a rosin sizing agent for acidic papers (AL120 available from Seiko PMC Corporation), and then, this pulp slurry was diluted with dilution water at pH4.5 to a concentration of 0.25%. Then, the pulp was converted into a paper having a basis weight of 50 g/m² in a test machine. The running pH was 4.5. The wet paper was dried using a drum dryer at 100° C. for 80 seconds.

(2) Preparation of a Neutral Newsprint Base Paper

To a deinked pulp slurry having a Canadian Standard Freeness (CSF) of 160 and a concentration of 2.5% were successively added 2% (bone dry weight basis) relative to pulp of calcium carbonate (TP121S available from Okutama Kogyo Co., Ltd.) and 0.25% (bone dry weight basis) relative to pulp of aluminum sulfate, and then this pulp slurry was diluted with dilution water at pH7.5 to a concentration of 0.25%. Then, the pulp was converted into a paper having a basis weight of 50 g/m² in a test machine. The running pH was 7.5. The wet paper was dried using a drum dryer at 100° C. for 80 seconds.

Example 10

An oxidized starch (MS3800 available from Nihon Shokuhin Kako Co., Ltd.) was diluted with water to a concentration of 10% and gelatinized at 95° C., and then combined with printability improving agent 1 described above to prepare a surface treating solution having solids concentrations of 6% oxidized starch and 0.3% printability improving agent 1 in the surface-treating agent. Thus prepared surface-treating agent was applied on the acidic newsprint base paper with No. 3 bar coater to give an acidic newsprint paper. The coating amount of the printability improving agent was 0.05 g/m² on a solids basis. Thus obtained acidic newsprint paper was used as a test piece and conditioned in an environment at constant temperature and humidity (23° C., relative humidity 50%) for 24 hours and measured for ink receptivity, drop test, contact angle and starch dissolution by the methods shown below. The results are shown in Table 2.

(Evaluation of Ink Receptivity)

Printing was performed using an RI printability tester (4 colors) available from Ishikawajima Industrial Machinery Co., Ltd. with high-viscosity aromatic-free inks available from Dainippon Ink and Chemicals, Incorporated as ecological offset printing inks after a water film has been formed between the rubber roll for printing the third color and the metal roll. Ink density was measured with a Machbeth densitometer. Higher values represent better ink receptivity.

(Evaluation of Drop Test)

A drop test was performed with a 1 μl drop of water according to the test method of J.TAPPI 33. Higher values represent better sizing.

(Evaluation of Contact Angle)

Using an automatic contact angle meter available from Kyowa Interface Science Co., Ltd., the contact angle was measured one second after a drop of water has been applied. Higher values represent better sizing.

(Evaluation of Starch Dissolution)

A paper sample cut into a rectangle of 2.5 cm×30 cm was rotated 30 times in water on an Adams Wet Rub Tester to dissolve starch. The amount of starch dissolved into water was expressed as the percentage of the amount of starch in the paper. Higher values represent less starch dissolution.

Examples 11-18, Comparative Examples 1-3

Coating and evaluations were performed in the same manner as in Example 10, except that printability improving agents 2-9 or printability improving agents 10-12 for comparative examples were used in place of printability improving agent 1. The results are shown in Table 2.

Example 19

Coating and evaluations were performed in the same manner as in Example 10, except that the surface-treating agent of Example 10 was adjusted to pH 7 with aqueous ammonia. The results are shown in Table 2.

[Table 2] TABLE 2 Printability Contact Starch improving Ink Drop test, angle, dissolu- agent receptivity second degree tion, % Example 10 1 1.00 45 101 18 Example 11 2 1.10 65 110 13 Example 12 3 1.08 60 108 13 Example 13 4 1.08 58 108 14 Example 14 5 1.11 63 110 14 Example 15 6 1.04 40 102 14 Example 16 7 1.06 38 100 15 Example 17 8 1.00 30 100 19 Example 18 9 0.99 28 97 19 Example 19 1 1.04 58 103 16 Comparative 10 0.91 17 105 22 example 1 Comparative 11 0.93 16 98 24 example 2 Comparative 12 0.96 26 102 23 example 3

Example 20

An oxidized starch (MS3800 available from Nihon Shokuhin Kako Co., Ltd.) was diluted with water to a concentration of 10% and gelatinized at 95° C., and then combined with printability improving agent 1 described above to prepare a surface treating solution having solids concentrations of 4% oxidized starch and 0.4% printability improving agent 1 in the surface-treating agent. Thus prepared surface-treating agent was applied on the neutral newsprint base paper with No. 3 bar coater to give a neutral newsprint paper. The coating amount of the printability improving agent was 0.08 g/m² on a solids basis. Thus obtained neutral newsprint paper was used as a test piece and conditioned in an environment at constant temperature and humidity (23° C., relative humidity 50%) for 24 hours and measured for ink receptivity, drop test, contact angle and starch dissolution by the methods described in Example 10. The results are shown in Table 3.

Examples 21-28, Comparative Examples 4-6

Coating and evaluations were performed in the same manner as in Example 20 except that printability improving agents 2-9 or printability improving agents 10-12 for comparative examples were used in place of printability improving agent 1. The results are shown in Table 3.

Example 29

Coating and evaluations were performed in the same manner as in Example 20 except that the surface-treating agent of Example 20 was adjusted to pH 7 with aqueous ammonia. The results are shown in Table 3.

[Table 3] TABLE 3 Printability Contact Starch improving Ink Drop test, angle, dissolu- agent receptivity second degree tion, % Example 20 1 0.99 39 102 19 Example 21 2 1.07 51 108 15 Example 22 3 1.05 46 107 16 Example 23 4 1.06 44 106 17 Example 24 5 1.08 50 108 18 Example 25 6 1.01 33 100 17 Example 26 7 1.04 30 99 17 Example 27 8 1.00 26 98 18 Example 28 9 0.97 20 97 19 Example 29 1 1.03 47 103 16 Comparative 10 0.85 7 91 28 example 4 Comparative 11 0.87 6 87 29 example 5 Comparative 12 0.89 10 89 26 example 6

The evaluation results of the acidic newsprint papers in Table 2 show that the newsprint papers of Examples 10-19 have better ink receptivity and less starch dissolution as compared with the newsprint papers of Comparative examples 1-3. The newsprint paper of Example 19 concomitantly using an alkaline material is shown to have clearly better ink receptivity and sizing performance as compared with Example 10.

The evaluation results of the neutral newsprint papers in Table 3 show that the newsprint papers of Examples 20-29 have better ink receptivity and clearly higher sizing effect as compared with the newsprint papers of Comparative examples 4-6. The newsprint paper of Example 29 concomitantly using an alkaline material is shown to have clearly better ink receptivity and sizing performance as compared with Example 20.

The following Examples 30-67 and Comparative examples 7-12 relate to printability improving agents according to the second aspect of the present invention.

1. Preparation of Printability Improving Agents

(1) Processes for Preparing Cationic Copolymers [A-1]

Synthesis Example 1

A 1-liter four-neck flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet tube was charged with 60 parts of styrene, 40 parts of dimethyl aminoethyl methacrylate, 2.5 parts of azobisisobutyronitrile and 44 parts of isopropyl alcohol, and maintained at 80° C. for 3 hours, and then 0.4 parts of azobisisobutyronitrile was added and the mixture was maintained at the same temperature for further 2 hours. Then, 17.0 parts of 90% acetic acid (100 mol % relative to dimethyl aminoethyl methacrylate) and 247 parts of water were added, and isopropyl alcohol was distilled off. Then, 48 parts of water and 23.5 parts of a quaternizing agent consisting of epichlorohydrin (100 mol % relative to dimethyl aminoethyl methacrylate) were added, and the mixture was maintained at 80° C. for 2 hours. Then, the mixture was diluted with water to give cationic copolymer (P-1) having a solids content of 20.7%. It should be noted that substantially no uncopolymerized monomer remained, and that little unreacted epichlorohydrin used as a quaternizing agent remained.

Synthesis Example 2

Cationic copolymer (P-2) having a solids content of 20.2% was obtained by the same procedure as in Synthesis example 1 except that the monomer composition was as shown in Table 4 for cationic copolymer (P-2) without using a quaternizing agent and that no quaternization reaction was performed.

Synthesis Examples 3-6

Cationic copolymers were obtained in the same manner as in Synthesis example 1 except that the type and amount of the hydrophobic monomer, the type and amount of the tertiary amino group-containing monomer, and the type and amount of the quaternizing agent used were varied as shown in Table 4. The solids contents of the resulting cationic copolymers (P-3) to (P-6) are shown in Table 4.

[Table 4] TABLE 4 Quaternary ammonium salt-containing Solids Cationic Hydrophobic monomer unit monomer unit content copolymer Type Parts Type Parts Type Parts Type Parts % by weight % P-1 St 60 — — DM 40 ECH 23.5 51.4 20.7 P-2 St 70 MMA 10 DMC 20 — — 20.0 20.2 P-3 St 60 EHA 20 DPA 20 ECH 11.8 28.5 20.1 P-4 IBMA 70 — — DPA 30 BTO 13.8 38.5 20.3 P-5 EHMA 40 — — DM 60 ECH 35.3 70.4 20.4 P-6 St 85 — — DM 15 ECH 8.8 21.9 19.3

In Table 4, symbols have the meanings below:

St: styrene, EHMA: 2-ethylhexyl methacrylate, MMA: methyl methacrylate, EHA: 2-ethylhexyl acrylate, IBMA: isobutyl methacrylate, DM: dimethyl aminoethyl methacrylate, DMC: dimethyl aminoethyl methacrylate quaternized with methyl chloride, DPA: dimethyl aminopropyl acrylamide, ECH: epichlorohydrin, BTO: butylene oxide.

Example 30

A reactor similar to that of Synthesis example 1 was charged with 192 parts of water, 121 parts of an aqueous solution of cationic copolymer [A-1] consisting of cationic copolymer (P-1) obtained in Synthesis example 1 (25 parts on a solids basis), 3 parts of surfactant [A-2] consisting of (N-1) shown in Table 2, hydrophobic monomer [B] consisting of 50 parts of styrene and 50 parts of normal butyl acrylate, and 5 parts by weight of 10% ammonium persulfate, and the mixture was heated to 80° C. with mixing/stirring under a nitrogen stream. The mixture was maintained at 80° C. for 2 hours to complete emulsion polymerization to give printability improving agent 13 having a solids concentration of 30.3%.

Examples 31-41

Printability improving agents 14-24 were obtained in the same manner as in Example 30, except that the type and amount of cationic copolymer [A-1], the type and amount of surfactant [A-2], and the type and amount of hydrophobic monomer [B] used were varied as shown in Table 5. The amounts of aggregates generated during polymerization reaction and the solids concentrations of the resulting printability improving agents are shown in Table 5.

[Table 5] TABLE 5 Cationic copolymer Surfactant Hydrophobic monomer Solids A-1 A-2 B content Type Content (%) Type Content (%) Type Content (%) % Example 30 P-1 25 N-1 3 St 50 30.3 BA 50 Example 31 P-1 100 — — St 50 29.5 BA 50 Example 32 P-1 50 N-1 5 St 50 30.4 BA 50 Example 33 P-1 100 N-1 3 St 50 30.2 BA 50 Example 34 P-1 50 N-1 10 St 50 30.2 BA 30 MMA 20 Example 35 P-1 50 N-2 3 St 50 30.9 BA 30 EHA 20 Example 36 P-1 50 N-3 3 St 60 30.0 MMA 20 EHA 20 Example 37 P-2 50 N-4 3 St 50 30.2 BA 50 Example 38 P-3 50 N-5 3 St 50 30.4 BA 50 Example 39 P-4 50 N-6 3 IBMA 50 30.2 BA 50 Example 40 P-5 50 N-7 3 St 50 30.4 BA 50 Example 41 P-6 50 N-1 5 St 50 30.0 BA 50

In Table 5, symbols have the meanings below:

P-1 to P-6: cationic copolymer (Synthesis examples 1-6)

N-1: C₁₂H₂₅—O-(EO)₂₀-H

N-2: C₁₈H₃₇—O-(EO)₂₀-H

N-3: C₉H₁₉—C₆H₄O-(EO)₂₀-H

N-4: CH₂═C(CH₃)COO-(EO)₂₀-C₁₂H₂₅

N-5: CH₂═C(CH₃)COO-(EO)₂₀-C₁₈H₃₇

N-6: C₁₂H₂₅—N⁺—(CH₃)₂(CH₂C₆H₅)Cl⁻

N-7: C₆H₅CH₂—N⁺—(CH₃)₃Cl⁻

St: styrene

BA: butyl acrylate

IBMA: isobutyl methacrylate

IBA: isobutyl acrylate

MMA: methyl methacrylate

EHA: 2-ethylhexyl acrylate

(Note) In N-1 to N-7, EO means ethylene oxide.

Synthesis Example 1 for Comparative Examples

A 1-liter four-neck flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet tube was charged with 44 parts of toluene, 50 parts of diisobutylene, 50 parts of maleic anhydride and 3.3 parts of 2,2′-azobisisobutyronitrile, and the mixture was heated with stirring to a temperature of 80° C. Then, the mixture was aged for 3 hours to complete the reaction. Then, a 48% aqueous potassium hydroxide solution (50 mol % relative to maleic anhydride), and 251 parts of water were added, and toluene was distilled off. Then, a 48% aqueous potassium hydroxide solution was added to a total of 100 mol % relative to maleic anhydride, and the solution was diluted with water to a copolymer concentration of 20% to give an aqueous potassium hydroxide solution of a water-soluble diisobutylene-maleic anhydride copolymer (printability improving agent 25 (for comparative examples)). The monomer composition ratio in the polymer was diisobutylene:maleic anhydride=50:50 by weight.

Synthesis Example 2 for Comparative Examples

A 1-liter four-neck flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet tube was charged with 35 parts of water, 65 parts of 95% isopropyl alcohol, a mixed monomer solution of 60 parts of styrene and 40 parts of maleic anhydride, and 3 parts of 2,2′-azobisisobutyronitrile, and the contents of the flask were heated with stirring to a temperature of 80° C. Then, the mixture was aged for 4 hours to complete the reaction. Then, isopropyl alcohol was distilled off, and after cooling, 50 parts of a 28% aqueous ammonia solution (100 mol % relative to maleic anhydride) was added, and the solution was diluted with water to a copolymer concentration of 20% to give an aqueous ammonia solution of a water-soluble styrene-maleic copolymer (printability improving agent 26 (for comparative examples)). The monomer composition ratio in the polymer was styrene:maleic anhydride=60:40 by weight.

Synthesis Example 3 for Comparative Examples

A 1-liter four-neck flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet tube was charged with 35 parts of water, 65 parts of 95% isopropyl alcohol, a mixed monomer solution of 70 parts of styrene and 30 parts of acrylic acid, and 3 parts of 2,2′-azobisisobutyronitrile, and the contents of the flask were heated with stirring to a temperature of 80° C. Then, the mixture was aged for 4 hours to complete the reaction. Then, isopropyl alcohol was distilled off, and after cooling, 25.3 parts of a 28% aqueous ammonia solution (100 mol % relative to maleic anhydride) was added, and the solution was diluted with water to a copolymer concentration of 20% to give an aqueous ammonia solution of a water-soluble styrene-acrylic copolymer (printability improving agent 27 (for comparative example)). The monomer composition ratio in the polymer was styrene:acrylic acid=70:30 (by weight).

Preparation of Newsprint Base Papers

(1) Preparation of an Acidic Newsprint Base Paper

To a deinked pulp slurry having a Canadian Standard Freeness (CSF) of 160 and a concentration of 2.5% were successively added 15% (bone dry weight basis) relative to pulp of talc (ND talc available from FUJI TALC INDUSTRIAL CO., LTD.), 1.5% (bone dry weight basis) relative to pulp of aluminum sulfate, and 0.05% (bone dry weight basis) relative to pulp of a rosin sizing agent for acidic papers (AL120 available from Seiko PMC Corporation), and then this pulp slurry was diluted with dilution water at pH4.5 to a concentration of 0.25%. Then, the pulp was converted into a paper having a basis weight of 50 g/m² in a test machine. The running pH was 4.5. The wet paper was dried using a drum dryer at 100° C. for 80 seconds.

(2) Preparation of a Neutral Newsprint Base Paper

To a deinked pulp slurry having a Canadian Standard Freeness (CSF) of 160 and a concentration of 2.5% were successively added 2% (bone dry weight basis) relative to pulp of calcium carbonate (TP121S available from Okutama Kogyo Co., Ltd.) and 0.25% (bone dry weight basis) relative to pulp of aluminum sulfate, and then this pulp slurry was diluted with dilution water at pH7.5 to a concentration of 0.25%. Then, the pulp was converted into a paper having a basis weight of 50 g/m² in a test machine. The running pH was 7.5. The wet paper was dried using a drum dryer at 100° C. for 80 seconds.

Example 42

An oxidized starch (MS3800 available from Nihon Shokuhin Kako Co., Ltd.) was diluted with water to a concentration of 10% and gelatinized at 95° C., and then combined with printability improving agent 13 described above to prepare a surface treating solution having solids concentrations of 7% oxidized starch and 0.2% printability improving agent 13 in the surface-treating agent. Thus prepared surface-treating agent was applied on the acidic newsprint base paper with No. 3 bar coater to give an acidic newsprint paper. The coating amount of the printability improving agent was 0.04 g/m² on a solids basis. Thus obtained acidic newsprint paper was used as a test piece and conditioned in an environment at constant temperature and humidity (23° C., relative-humidity 50%) for 24 hours and measured for ink receptivity, drop test, contact angle and starch dissolution by the methods described above. The results are shown in Table 5.

Examples 43-53, Comparative Examples 7-9

Coating and evaluations were performed in the same manner as in Example 42 except that printability improving agents 14-24 or printability improving agents 25-27 for comparative examples were used in place of printability improving agent 13. The results are shown in Table 5.

Example 54

Coating and evaluations were performed in the same manner as in Example 42 except that the surface-treating agent of Example 42 was adjusted to pH 7 with aqueous ammonia. The results are shown in Table 6.

[Table 6] TABLE 6 Printability Contact Starch improving Ink Drop test, angle, dissolu- agent receptivity second degree tion, % Example 42 13 1.00 35 99 17 Example 43 14 1.01 40 102 16 Example 44 15 1.07 50 108 13 Example 45 16 1.05 51 108 14 Example 46 17 1.06 48 106 14 Example 47 18 1.10 60 110 12 Example 48 19 1.10 58 108 13 Example 49 20 1.04 45 105 14 Example 50 21 1.11 62 111 12 Example 51 22 1.09 56 110 13 Example 52 23 1.03 41 105 14 Example 53 24 1.00 32 98 18 Example 54 13 1.06 44 104 15 Comparative 25 0.92 20 103 21 example 7 Comparative 26 0.93 19 98 23 example 8 Comparative 27 0.95 27 100 24 example 9

Example 55

An oxidized starch (MS3800 available from Nihon Shokuhin Kako Co., Ltd.) was diluted with water to a concentration of 10% and gelatinized at 95° C., and then combined with printability improving agent 13 described above to prepare a surface treating solution having solids concentrations of 5% oxidized starch and 0.3% printability improving agent 13 in the surface-treating agent. Thus prepared surface-treating agent was applied on the acidic newsprint base paper with No. 3 bar coater to give a neutral newsprint paper. The coating amount of the printability improving agent was 0.07 g/m² on a solids basis. Thus obtained neutral newsprint paper was used as a test piece and conditioned in an environment at constant temperature and humidity (23° C., relative humidity 50%) for 24 hours and measured for ink receptivity, drop test, contact angle and starch dissolution by the methods described above. The results are shown in Table 7.

Examples 56-66, Comparative Examples 10-12

Coating and evaluations were performed in the same manner as in Example 55, except that printability improving agents 14-24 or printability improving agents 25-27 for comparative examples described above were used in place of printability improving agent 13 described above. The results are shown in Table 7.

Example 67

Coating and evaluations were performed in the same manner as in Example 55, except that the surface-treating agent of Example 55 was adjusted to pH 7 with aqueous ammonia. The results are shown in Table 7. TABLE 7 Printability Contact Starch improving Ink Drop test, angle, dissolu- agent receptivity second degree tion, % Example 55 13 0.96 25 97 18 Example 56 14 0.97 31 100 16 Example 57 15 1.02 39 107 14 Example 58 16 1.00 42 107 15 Example 59 17 1.02 37 104 14 Example 60 18 1.04 51 110 13 Example 61 19 1.04 47 107 13 Example 62 20 0.99 33 105 14 Example 63 21 1.06 53 110 13 Example 64 22 1.04 43 108 13 Example 65 23 1.01 34 105 15 Example 66 24 0.97 23 96 19 Example 67 13 1.02 35 104 16 Comparative 25 0.84 6 90 28 example 10 Comparative 26 0.85 5 87 29 example 11 Comparative 27 0.88 10 89 26 example 12

The evaluation results of the acidic newsprint papers in Table 6 show that the newsprint papers of Examples 42-53 have better ink receptivity and less starch dissolution as compared with the newsprint papers of Comparative examples 7-9. The newsprint paper of Example 54 concomitantly using an alkaline material is shown to have clearly better ink receptivity and sizing performance as compared with Example 42.

The evaluation results of the neutral newsprint papers in Table 7 show that the newsprint papers of Examples 55-66 have better ink receptivity and clearly higher sizing effect as compared with the newsprint papers of Comparative examples 10-12. The newsprint paper of Example 67 concomitantly using an alkaline material is shown to have clearly better ink receptivity and sizing performance as compared with Example 55. 

1. A printability improving agent characterized in that it comprises a cationic copolymer comprising one or more hydrophobic monomer unit(s) selected from the group consisting of: (1) alkyl acrylates and/or alkyl methacrylates (2) dialkyl diesters (3) vinyl esters (4) N-alkyl acrylamides and/or N-alkyl methacrylamides (5) methyl vinyl ethers and a quaternary ammonium salt-containing monomer unit.
 2. A surface-treating agent characterized in that it comprises the printability improving agent of claim 1 and one or more water-soluble polymer material(s) selected from the group consisting of: (1) various modified starches (2) polyvinyl alcohols (3) cellulose derivatives.
 3. A paper characterized in that it is obtained by applying the printability improving agent of claim 1 or the surface-treating agent on the surface of a base paper.
 4. The paper of claim 3 characterized in that the base paper is a newsprint base paper prepared by a neutral papermaking process.
 5. A printability improving agent comprising (I) a copolymer obtained by polymerizing one or more hydrophobic monomer unit(s) selected from the group consisting of: (1) styrenes (2) alkyl acrylates and/or alkyl methacrylates (3) dialkyl diesters (4) vinyl esters (5) N-alkyl acrylamides and/or N-alkyl methacrylamides (6) methyl vinyl ethers and a quaternary ammonium salt-containing monomer unit to give a cationic copolymer, which is further polymerized with one or more hydrophobic monomer(s) selected from the group shown above, or (II) a copolymer obtained by polymerizing the cationic copolymer obtained by polymerization of the hydrophobic monomer unit(s) and a quaternary ammonium salt-containing monomer unit with one or more hydrophobic monomer(s) selected from the group shown above in the presence of a surfactant.
 6. A surface-treating agent comprising the printability improving agent of claim 5 and one or more water-soluble polymer material(s) selected from the group consisting of: (1) various modified starches (2) polyvinyl alcohols (3) cellulose derivatives.
 7. A paper characterized in that it is obtained by applying the printability improving agent of claim 5 or the surface-treating agent on the surface of a base paper.
 8. The paper of claim 7 characterized in that the base paper is a newsprint base paper prepared by a neutral papermaking process. 